1. Field of the Invention
The present invention relates to a wafer dividing method for dividing a wafer into individual devices along a plurality of crossing streets formed on the front side of the wafer, wherein the devices are respectively formed in a plurality of areas partitioned by the streets.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing streets (division lines) are formed on the front side of a substantially disk-shaped semiconductor wafer to partition a plurality of areas where devices such as ICs, LSIs, liquid crystal drivers, and flash memories are respectively formed. The wafer is cut along the streets to divide these areas from each other along the streets, thereby producing the individual devices.
As a method of dividing the wafer along the streets, a laser processing method using a pulsed laser beam having a transmission wavelength to the wafer has been proposed. In this laser processing method, the pulsed laser beam is applied to the wafer along the streets in the condition where a focal point of the pulsed laser beam is set inside the wafer in a subject area to be laser-processed. In such a wafer dividing method using laser processing, the pulsed laser beam having a transmission wavelength to the wafer is applied to the wafer from one side thereof in the condition where the focal point is set inside the wafer, thereby continuously forming a modified layer inside the wafer along each street. By forming the modified layer along each street, the strength of the wafer along the modified layer is reduced. Accordingly, by applying an external force to the wafer along each street, the wafer can be broken along each street to obtain the individual devices. According to this dividing method, the width of each street can be reduced (see Japanese Patent No. 3408805, for example).
However, in the case that the surface of each street is covered with a film such as a metal film, fluorosilicate glass film, silicon oxide based passivation film (SiO2, SiON), polyimide (PI) based polymer film, fluorine based polymer film, and fluorinated amorphous carbon based compound film, the following problem arises. That is, the substrate of the wafer can be divided by applying a pulsed laser beam having a transmission wavelength to the substrate along each street in the condition where the focal point of the pulsed laser beam is set inside the substrate to thereby form a modified layer inside the substrate along each street. However, the film formed on the surface of each street cannot be divided by this method.